A national consumer group says the U.S. Food and Drug Administration should set minimum sanitary and safety standards for pallets used to transport food, after tests revealed the presence of bacteria that cause food poisoning.

"We believe it is essential to ensure that pathogens are not introduced at any step along the food transport system, from farm to fork," Sally Greenberg, National Consumers League executive director, said in a statement.

The recommendations follow recent tests conducted by the league on pallets -- usually wooden structures seated at the bottom of stacked products and used by forklifts -- to determine whether they may be carriers of pathogens.

In January, McNeil Consumer Healthcare recalled products due to a moldy odor that caused some users nausea, stomach pain, vomiting or diarrhea. The company ascribed the problem to "the breakdown of a chemical that is sometimes applied to wood that is used to build wood pallets that transport and store product packaging materials."

The NCL tested pallets for a number of food-borne pathogens, including E. coli and Listeria, and found 10% of the wooden pallets tested positive for E. coli (though not the most virulent strain, E. coli O157:H7). Testing was conducted in late April on 70 wood and 70 plastic pallets used to transport food in the greater Houston, Tex., Miami and Tampa, Fla., areas. The NCL shipped the samples overnight to an independent microbiology lab that provides testing services for industrial, regulatory, and law-enforcement clients.

"Our testing of pallets has shown that these relatively unregulated but crucial parts of the food transportation system can and do harbor dangerous pathogens that could potentially contaminate the food supply," Greenberg said.

In addition to the presence of E. coli, a common intestinal bacteria that can cause food poisoning, 2.9% of the wood pallets tested positive for Listeria. Half of these, when further tested, contained Listeria monocytogenes, one of the most virulent pathogens. This strain is linked to a 20 to 30% rate of clinical infection resulting in death, and causes approximately 2,500 illnesses and 500 deaths in the United States every year. Listeriosis is also more likely to cause death than any other food-borne bacterial pathogen.

Of the 70 plastic pallets tested, the NCL said, one came back positive for E. coli. None of the other plastic pallets tested positive for pathogens. High aerobic plate counts, which reflect unsanitary conditions, were found on approximately one third of the wood pallets and one fifth of the plastic ones.

"With approximately two billion pallets currently in circulation in the United States, the presence of dangerous pathogens on even a small percentage of those pallets presents a potential threat to the safety of the food supply," Greenberg wrote to the FDA .

Although both types of pallets tested positive for pathogens, wooden pallets contained far more for a number of reasons. Unlike plastic, wooden pallets absorb water, harbor bacteria and are difficult to fully clean, making it easier for them to contaminate food. The NCL's test also revealed wood pallets are more likely to be stored outside and exposed to weather, rodents, bird droppings and insects. Splinters on wooden pallets can also damage packaging, creating an opening for pathogens.

In a just-issued report prepared for the FDA, Eastern Research Group, Inc. highlights the use of "good quality pallets" as a preventive measure. The agency has said it will use the report to inform the development of new rules to increase the safety of food during transport.